142 THE HAUNTS OF LIFE 



its ancestors were deep-water fishes. Similarly, 

 though the flounder is often found in rivers 

 20 miles from the sea, it does not spawn in 

 fresh water, it must go back to its old home in 

 the shallow sea. It will be interesting to think 

 out some cases that seem to break this rule. 



It is also to be remembered that some ani- 

 mals are at present making the transition from 

 salt water to fresh. The flounder is a case in 

 point, undoubtedly a marine fish, but be- 

 coming more and more accustomed to the 

 rivers. The quaint Manatee, included with 

 the Dugong in the small order of mammals, 

 known as sea-cows, or Sirenia, is typically a 

 coastal mammal, but it goes far up the rivers, 

 and it is now found, for instance, in the Ever- 

 glades of Florida, a far cry from the sea. 



In any case we should not think of the 

 fresh-water fauna as a fixed and finished as- 

 semblage of animals. It is a noteworthy fact 

 that many fresh-water animals spend only a 

 part of their lives in the fresh water. Some 

 of these seem to be still in process of accus- 

 toming themselves to it, others to be leaving 

 it for salt water, and others again are appar- 

 ently on the way to becoming land animals. 



How can we tell in which direction a par- 



